Let there be no mistake that I oppose this law. However, you are wrong in saying that it would be unique among democratic countries. Article 25 of the French civil code, for instance, permits French nationals to be stripped of citizenship upon (among other things) conviction of a terrorist offense, conviction of draft evasion or commission of acts abroad that are detrimental to the interest of France. Another section of the same code, Article 23-8, provides for loss of nationality if a French citizen provides aid to a foreign country or international organization of which France is not a member, and doesn't stop doing so after being ordered to cease by the French government. Article 20 of the Code of Greek Nationality allows the interior minister to strip the citizenship of a Greek who "while living abroad has performed acts beneficial for a foreign state but incompatible with the quality of a Greek citizen." Unfortunately this is a sin of many nations, not just one.
In Qatar, Kerry seeks to convince Gulf Arabs on Iran deal (Reuters)
from the article: Conditional citizenship